1. Field of the Invention
The present invention relates to data transfer device and method.
2. Description of the Related Art
The client-server type information system having a server for providing various services on a network and a client for requesting services to the server is widely used. The World Wide Wed system (referred hereafter as Web) for carrying out communications by utilizing the HTTP (HyperText Transfer Protocol) on the internet is the very widely used client-server type information system. Normally, in the Web, a server program is operated on the server and a prescribed program such as a Web browser is operated on the client.
In the client-server type information system such as Web, the services are provided by the communications between the client and the server. Consequently, the communication bandwidth between the client and the server tends to become a bottleneck of the entire system. For this reason, the cache technique is usually used for the purpose of reducing the network load.
In the case of the Web, the Web browser or the like that is operated on the client often utilizes the cache function, to cache recently accessed data. In the Web system, the access is made by specifying the information or the service by a URL (Uniform Resource Locator), so that the cache on the client stores those which are cachable among data returned as results of requesting the information or the service to the Web server in the past, in the cache in correspondence to their URLs. Then, when there is a request for the information or the service of the same URL as that present in the cache, that data is returned such that the communication with the server can be eliminated, as long as it is possible to judge that the data in the cache is not obsolete yet.
Also, in the case of using LAN (Local Area Network), the cache function is often provided at a proxy server that is provided between the LAN and the Internet. The cache of the client described above is a cache dedicated to the user of that client, but the cache of the proxy server on the LAN is operated as a cache snared by a plurality of users, so that the cache works even in the case of accessing the URL that was accessed by the other client in the past.
The caching targets of these caches are static contents. In the past, many of the information and the services disclosed on the Web are largely static contents for which the information updating frequency is not very high and which are disclosed to the unspecified many, so that the checking of the presence/absence of the cache on the basis of URL was sufficiently effective.
However, as the system in which the user uses the Web browser to access the information and the service on the server via the network such as the Web based ASP (Application Service Provider) becomes widespread, the data that cannot be handled by the above described cache technique are increasing.
In order to deal with such problems, the cache technique using a fingerprint (FP) compression has been proposed in the commonly assigned, co-pending U.S. patent application Ser. No. 10/092,540.
In the U.S. patent application Ser. No. 10/092,540, the FP compression processing is carried out between a proxy server on the client side (CSP: Client Side Proxy) and a proxy server on the Web server side (SSP: Server Side Proxy), so that two proxy servers are necessary and there has been a problem that the network configuration becomes complicated.
For example, in the case of the portable terminal utilizing the Mobile IP technique, the communication path from the portable terminal to the Web server and the communication path from the Web server to the portable terminal are different so that it is difficult to use the CSP.